Block copolymers are generally thought to be polymeric chains containing alternating segments or "blocks" of homopolymers or copolymers where each block differs materially from the adjacent block. Block copolymers may be di-block copolymers such that blocks of (A) alternate with blocks of (B) along the polymer chain or they may be multiblock copolymers wherein blocks of two different polymers are present in the polymer chain in alternate or an ABA configuration. An ABA tri-block unit is one where the first polymer A is present on either side of second polymer B creating a repeating three block sequence.
Some of the more versatile block copolymers known in the art are styrene-isoprene-styrene, (SIS) and styrene-butadiene-styrene (SBS) triblock copolymers. In general, block copolymers have either elastomeric or thermoplastic elastomeric qualities and are used in a wide variety of applications. Block copolymers may be subject to various modification or functionalization reactions to improve or alter their properties. One of the reactions which may be performed on some of these block copolymers is a hydrogenation reaction wherein the unsaturations within the blocks are removed. For example, in a styrene-isoprene-styrene block copolymer a homogeneous catalyst may be utilized to selectively hydrogenate the unsaturations in the isoprene to produce what is essentially an ethylene propylene block while leaving the styrene blocks saturated. This particular configuration has found many uses and is known commercially as KRATON G..TM.
Hydrogenation of the isoprene and the polystyrene blocks in a multiblock copolymer has also been reported in the art. U.S. Pat. No. 3,333,024 to Haefele discloses that a styrene-isoprene-styrene block copolymer having a combined styrene content of 22% by weight can be hydrogenated by suspending the block copolymer in cyclohexanes and contacting it with a catalyst of nickel on kieselguhr at a pressure of 500 psig and at a temperature of 145.degree.-55.degree. C. for thirteen hours. The resulting hydrogenated block copolymer had 98% hydrogenation of the polystyrene blocks. The block copolymers were reported to have improved tensile properties over the unhydrogenated block copolymers, However, in Chapter 14 of Thermoplastic Elastomers, a comprehensive review, Ed. N. R. Legge, et al., Hanser Publishers, New York, 1987, this class of hydrogenated block copolymers was described as being generally poor. These hydrogenated materials are generally described as having an interaction parameter so severely reduced that at only slightly elevated temperatures the polymer loses all strength and appears to be homogeneous mixture. Thus, the good tensile strength of U.S. Pat. No. 3,333,024 appears to be limited to a low temperature end use range.
The hydrogenation of polymers is a known technique. There are two typical techniques, homogeneous and heterogeneous that have been shown effective for obtaining saturated polymers. Homogeneous hydrogenation yields high conversions, however, this method sometimes causes chain scission and often leads to metal contamination due to a catalyst extraction difficulties. Heterogeneous hydrogenation yields high conversions and in certain cases is more tractable than homogeneous hydrogenation due to minimal chain scission and no metal contamination and the ease of catalyst extraction. Furthermore, supported heterogenous transition metal catalysts are recyclable with no byproducts unlike homogeneous extraction products which generate large amounts of waste product. Heterogeneous hydrogenation has been used to saturate many types of polydienes including 1,4 and 3,4-poly(isoprene) and 1,2 and 1,4-polybutadiene. (Zhongde, X; et al., Macromolecules, 1983, 16, 925.)
Thus, hydrogenated block copolymers having good end-use properties such as high order/disorder transition temperatures, (T.sub.ODT) or high glass transition temperatures (Tg's) and methods to make them are desirable.